1. Field of the Invention
The present invention relates to a new organophosphate dispersing agent and a thermosetting composition, comprising a thermosetting unsaturated polyester resin containing a monomer which may subsequently be copolymerized with the polyester resin, or an alkyd-, acrylic- or phenolic-type molding resin, a pulverulent mineral filler, and a dispersing agent. The dispersing agent makes it possible to obtain highly-filled thermosetting molding compositions having no yield point and low viscosities under very low shear ratios.
2. Discussion of the Background
During the fabrication of molded articles from a composition based on thermosetting resins of unsaturated polyester, alkyd, acrylic, or phenolic-type molding resins, in accordance with one of the conventional sheet-molding (sheet molding composition--SMC) and bulk molding (bulk molding composition--BMC) techniques, it becomes increasingly necessary to increase the quantity of mineral filler in order to reduce the cost of the molded articles. It is also necessary to preserve mechanical, thermal, dielectric, and aesthetic properties of the resins, as well as to obtain a viscosity of the mixture which is as low as possible at high and low shear ratios. In fact, the lack of a yield point allows the resin to be easily worked at all stages of the molding operation. In order to add fillers to these resins, the use of conventional organophosphate dispersing agents is well known.
Patent Applications JP 61-101527, JP 62-207337, JP 62-235353 disclose the addition of organophosphates to mixtures containing a maximum of 100 parts filler for 100 parts resin. For greater concentrations of mineral filler ranging up to 65%, U.S. Pat. No. 4,183,843 claims the use of polar esters of phosphoric acid. When used in small proportions, these products reduce the viscosity of the mixture of calcium carbonate and/or aluminum hydroxide and/or titanium dioxide and/or silicon dioxide and/or clay with unsaturated polyester-type resins under high shear ratios. However, the viscosity under very low shear ratios remains very great and there exists a yield point which makes the formulations difficult to handle. Furthermore, it has been observed that the viscosity of the thermosetting composition increases in a directly proportional manner to the quantity of these polar phosphated esters used, resulting in a thickening effect.